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MCAT > concept 5e > Flashcards

concept 5e Flashcards

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1
Q

system

A

the matter that is being observed in the reaction

total amount of reactants and products in a reaction

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2
Q

surroundings

A

or environment

everything outside of the system

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3
Q

categories of systems

A

isolated
closed
open

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4
Q

isolated system

A

system cannot exchange energy or matter with the surroundings
exp. an insulated bomb calorimeter

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5
Q

closed system

A

system can exchange energy but cannot exchange matter with the surroundings
exp. a steam radiator

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6
Q

open system

A

system can exchange both energy and matter with the surroundings
exp. pot of boiling water

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7
Q

energy exchange

A

exchange of heat and work

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8
Q

process

A

when a system experiences a change in one or more of its properties it undergoes a process
change can be change in concentrations of reactants or products, temp, or pressure
a change of the state of a system

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9
Q

First law of thermodynamics

A

states that the total energy of a system and its surroundings remains constant
delta U=Q-W
delta U is the change in internal energy of a system, Q is heat added, W is work done by the system

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10
Q

isothermal process

A

occur when the system’s temperature is constant
constant temp implies that total internal energy is constant
forms a hyperbolic curve on pressure-volume graph

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11
Q

adiabatic process

A

occur when no heat is exchanged b/w the system and the environment
thermal energy is constant
the change in internal energy is equal to work done on the system (-W)
hyperbolic curve on P-V graph

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12
Q

isobaric process

A

occur when the pressure of the system is constant
appears as a flat line on a P-V graph
common bc it is easy to control temp and pressure

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13
Q

isovolumetric (isochoric) process

A

processes experience no change in volume
the gas neither expands or compresses, no work is performed
the change in internal energy is equal to the heat added to the system
appears as a vertical line on P-V graph

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14
Q

spontaneous process

A

process that occur by itself without having to be driven by energy from an outside source
may not happen quickly and may not go to completion
tend to have high activation energies

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15
Q

state functions

A

properties that describe the system in an equilibrium state
cannot describe the process of the system, how the system got to its equilibrium
useful for comparing one equilibrium state to another

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16
Q

process function

A

the pathway taken from one equilibrium state to another described quantitatively
most important are work (W) and heat(Q)

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17
Q

values of state functions

A

pressure (P), density, temp (T), volume (v), enthalpy (H), internal energy (U), Gibbs free energy (G), entropy (S)
“when I’m under Pressure and feel Dense, all I want to do is watch TV and get HUGS”

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18
Q

standard conditions

A

standard values defined for measuring the enthalpy, entropy, and Gibbs free energy of a reaction
298 K (25 deg C)
1 atm pressure
1 M concentrations
dont confuse with standard temperature and pressure (STP)

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19
Q

standard temperature and pressure

A

temp is 273 K (0 deg C)
pressure is 1 atm
used for ideal gas calculations

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20
Q

standard state

A 
most stable form of a substance under standard conditions 
H2(g)
H20(l)
NaCl(s)
O2(g)
C(s,graphite)
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21
Q

phase diagrams

A

graphs that show the standard and nonstandard states of matter for a given substance in an isolated system
determined by temperatures and pressures

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22
Q

phase changes

A

changing between a solid, liquid, or gas
are reversible
an equilibrium of phases eventually reached at any given combination of temperature and pressure

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23
Q

phase equilibria

A

analogous to the dynamic equilibria or reversible chemical reactions
the concentrations of reactants and products are constant bc the rates of the forward and reverse reactions are equal

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24
Q

liquid phase

A

molecules are relatively free to move
some near the surface have enough kinetic energy to leave the liquid phase
each time a particle leaves the temp of remaining liquid decreases

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25
Q

evaporation

A

vaporization
the process where a molecule has enough kinetic energy to leave the liquid phase and escape into the gaseous phase
endothermic process

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26
Q

boiling

A

specific type of vaporization that occurs only under certain conditions
rapid bubbling of the entire solution with rapid release of liquid to gas particles
only occurs above the boiling point of a liquid and involves vaporization through the entire volume of liquid

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27
Q

condensation

A

in a covered container the escaping molecules are trapped above the solution
these molecules exert a countering pressure
this forces some of the gas back into the liquid phase
facilitated by lower temperature or higher pressure

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28
Q

boiling point

A

the temp at which the vapor pressure of the liquid equals the ambient pressure
ambient pressure –> external, applied, incident, atmospheric

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29
Q

gas-liquid equilibrium processes

A

evaporation
vaporization
boiling
condensation

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30
Q

solid phase

A

atoms or molecules are confined to specific locations
each molecule can undergo motions about some equilibrium position
these vibrations increase when heat is applied

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31
Q

energy microstates

A

availability of these microstates increase as the temperature of the solid increases
that molecules have greater freedom of movement and energy disperses

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32
Q

fusion

A

or melting
process from solid to liquid
molecules in solid phase absorb enough energy the 3D structure of the solid will break down, and the molecules will escape into liquid phase
temperature at which this occurs is called melting point

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33
Q

solidification

A

or crystallization, or freezing
reverse process of fusion
from liquid to solid
temperature at which this occurs is called the freezing point

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34
Q

liquid-solid equilibrium processes

A

fusion or melting

solidification, crystallization, or freezing

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35
Q

sublimation

A 
when solid goes directly into the gas phase 
dry ice (solid CO2) sublimes at room temperature and atmospheric pressure
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36
Q

deposition

A

reverse transition

from gaseous to solid phase

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37
Q

cold finger

A

device used in organic chem labs
used to purify a product that is headed under reduced pressure
this causes it to sublimate

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38
Q

gas-solid equilibrium processes

A

sublimation

deposition

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39
Q

lines of equilibrium

A

phase boundaries
lines on a phase diagram
indicate the temperature and pressure values for the equilibria b/w phases
divide the diagram into 3 regions corresponding to the 3 phases
represent phase transformations

40
Q

triple point

A

point at which the three phase boundaries meet

this is the temp and pressure at which the three phases exist in equilibrium

41
Q

critical point

A

the phase boundaries terminate at this point

this is the temp and pressure above which there is no distinction between phases

42
Q

temperature (T)

A

related to the average kinetic energy of the particles of a substance
was we scale how hot or cold something is

43
Q

thermal energy (enthalpy)

A

average kinetic energy of the particles in a substance

we must also consider how much substance is present

44
Q

heat (Q)

A

transfer of energy from one substance to another as result of their difference in temperature

45
Q

heat vs temp

A

heat is specific form of energy that can enter or leave a system
temp is a measure of the average kinetic energy of the particles in a system

46
Q

zeroth law of thermodynamics

A

implies that objects are i thermal equilibrium only when their temperatures are equal
this leads us to believe that heat is a process function not a state function

47
Q

endothermic process

A

system absorbs heat

delta Q>0

48
Q

exothermic process

A

system releases heat

delta Q<0

49
Q

unit of heat

A

joule (J) or calorie (cal)

1 cal=4.184 J

50
Q

enthalpy

A

delta H

equivalent to heat (Q) under constant pressure

51
Q

calorimetry

A

process of measuring transferred heat
2 basics types: constant-pressure calorimetry and constant-volume calorimetry
coffee-cup calorimeter is an example of a constant-pressure calorimeter
bomb calorimeter is an example of a constant-volume calorimeter

52
Q

q=mc(deltaT)

A

the heat abosorbed or released in a given process

m is mass, c is specific heat of substance, delta T is the change in temp (in C or K)

53
Q

specific heat

A

the amount of energy required to raise the temperature of one gram of a substance by one degree C or one K
generally provided on test day
except for H20–>c(H20)=1cal/g*K

54
Q

heat capacities

A

product m*c (mass times specific heat)

55
Q

constant-pressure calorimeter

A

an insulated container covered with a lid and filled with a solution in which a reaction or some physical process is occurring
pressure is constant and temperature is measured as run progresses
should be sufficient thermal insulation to ensure accurate temp measurement
coffee-cup calorimeter

56
Q

bomb calorimeter

A

or decomposition vessel
type of constant-pressure calorimetry
sample of matter placed in steel decomposition vessel filled with almost pure oxygen gas
vessel then placed in insulated container holding mass of water
vessel ignited with electric ignition mechanism
material combusts in presence of oxygen and the heat that evolves is the heat of the combustion reaction

57
Q

heating curves

A

as compound is heated, the temp rises until melting or boing point
the it remains the same as compound is converted to next phase
once sample is converted the temp begins to rise again until reaches next transition phase
phase change regions do not change temp is we can’t use q=mc(deltaT)

58
Q

q=mL

A

used to find q during phase change

m is mass and L is latent heat, general term for enthalpy of isothermal process

59
Q

enthalpy (H)

A

heat content of a system at constant pressure
state function, so we can calculate the change in enthalpy for a system undergoing a process
done by subtracting the H of reactants from the H of products
positive delta H is an endothermic process, negative delta H is exothermic process

60
Q

standard enthalpy of formation

A

the enthalpy required to produce one mole of a compound from its element in their standard states

61
Q

standard heat of a reaction

A

enthalpy change accompanying a reaction being carried out under standard conditions
calculated by taking the difference b/w the sum of the standard heats of formation for the products and subtracting the sum of standard heats of formation for the reactants

62
Q

Hess’s Law

A

states that enthalpy change of reactions are additive
when thermochemical equations are added to get net equation the corresponding gets of reaction are also added to give net heat of rxn
applies to all state functions including entropy and Gibbs free energy

63
Q

bond dissociation energies

A

the average energy this si required to break a particular type of bond between atoms in the game phase
endothermic process

64
Q

bond formation energies

A

opposite of bond breaking
has the same magnitude of energy but is negative rather than positive
energy is released when bonds are formed

65
Q

standard heat of combustion

A

enthalpy change associated with the combustion of a fuel

66
Q

entropy

A

measure of the spontaneous dispersal of energy at a specific temperature
how much energy is spread out, or how widely spread out energy becomes in a process
deltaS=Qrev/T
Qrev is the heat that is gained or lost, T is the temp in K
when heat is distributed into a system entropy increases, when it is distributed out of a system entropy decreases

67
Q

second law of thermodynamics

A

states that all spontaneous processes lead to an increase in entropy of the universe
energy spontaneously disperses from being localized to becoming spread out if it is not hindered from doing so

68
Q

Gibbs free energy (G)

A

the energy of a system available to do work
change in free energy can be determined for a given reaction equation from the enthalpy change, temperature, and entropy change
negative deltaG denotes spontaneous reaction, positive deltaG denotes a nonspontaneous reaction

69
Q

exergonic process

A

movement toward equilibrium position
decrease in Gibbs free energy (deltaG<0)
spontaneous

70
Q

endergonic process

A

movement away from the equilibrium position
increase in Gibbs free energy (deltaG>0)
nonspontaneous

71
Q

effects of deltaH, deltaS and T on spontaneity

A

+deltaH, +deltaS–>spontaneous at high T
+deltaH, -deltaS–>nonspontaneous at all T
-deltaH, +deltaS–>spontaneous at all T
-deltaH,-deltaS–>spontaneous at low T

72
Q

standard free energy

A

free energy change of reactions measured under standard conditions
can be derived from standard free energy of formation of products minus reactants
can also be determined from equilibrium constants

73
Q

deltaGrxn=-RTlnKeq

A

free energy from equilibrium constant
R is ideal gas constant, T is temp in K, Keq is the equilibrium constant
evaluate free energy change and spontaneity of reaction
higher Keq, more positive ln, more negative standard free energy change, more spontaneous

74
Q

collision theory of chemical kinetics

A

states that the rate of a reaction is proportional the the number of collisions
effective collision, that leads to product, occurs only if the molecules collide w/ each other in correct orientation w/ enough energy
rate=Z*f (Z is # of collisions, f is fraction of effective collisions)

75
Q

reaction concentrations

A

greater concentration of reactions, the greater the number of effective collisions, increase in reaction rate
direct relationship

76
Q

temperature

A

reaction rate will increase as the temperature increases
all reactions are temperature dependent and experience an optimal temperature for activity
usually b/w 30-40 deg C
if it exceeds optimal temp the catalyst will denature and the rxn rate plummets

77
Q

solvent

A

generally polar solvents are preferred
their dipole polarized the reactants weakening the bonds and this allows for effective collisions and a reaction to occur

78
Q

catalyst

A

increase the reaction rate by decreasing the activation energy for the reaction
are not consumed in the reaction

79
Q

rate law

A

for forward irreversible rxns the rate is proportional to the concentration of reactants
aA+bB–>cC+dD
rate=k[A]^a[B]^b

80
Q

zero-order reaction

A

reaction in which the rate of formation of product C is independent of changes in concentration of any of the reactants
rate=k[A]^0[B]^0=k
on graph of concentration vs time curve, slope is linear and opposite (negative) of k

81
Q

first-order reaction

A

rate that is directly proportional to only one reactant
rate=k[A] or rate=k[B]
shows a nonlinear graph of conc. vs time, this proves that the rate of formation of products is dependent on conc. of reactant
plotting ln[A] vs. time reveals a linear graphe where k=-slope

82
Q

second-order reaction

A

rate that is proportional to either the concentrations of 2 reactants or the square f the concentration of a single reactant
rate=k[A][B] or rate=k[A]^2 or rate=k[B]^2
nonlinear graphs for conc. vs. time, decreases faster than first order (greater exponential decline)
if plot 1/[A] vs. time get a linear graph where k=slope

83
Q

higher-order reaction

A

very few noteworthiness reactions
bc it is far more rate for 3 particles to collide simultaneously with correct orientation and sufficient energy to undergo a reaction

84
Q

mixed-order reaction

A

non-integer orders (fractions)
a reaction in which the reaction order changes over time in the rate law
more specifically described as broken-order

85
Q

law of mass action

A

states that if the system is at equilibrium at a constant temperature than the ratio is constant:
Keq=[C]^c[D]^d/[A]^a[B]^b=[prod]/[react]
defines the position of equilibrium

86
Q

at equilibrium…

A

the rate of the forward reaction equals the rate of the reverse reaction
entropy is at a maximum
Gibbs free energy is at a minimum
linking thermodynamic and kinetics

87
Q

reaction quotient (Q)

A

has the same form as the equilibrium constant but the concentrations of products and reactants may not be at equilibrium
when compared to Keq it dictates the direction a reaction will proceed spontaneously
Q=[C]^c[D]^d/[A]^a[B]^b=[prod]/[react] during any point in the reaction

88
Q

comparing Keq and Q

A

QKeq: reaction proceeds in the reverse direction toward reactants, greater conc. of products, deltaG>0 (endergonic)

89
Q

properties of law of mass action

A
  1. concentrations of pure solids and pure liquids don’t appear in equil. constant expression
  2. Keq (equil. constant) is temperature-dependent
  3. the larger Keq, the equilibrium position lies further to the right (toward products), so more products at equil. than reactants
  4. if equilibrium constant for rxn in one direction is Keq, for the reverse reaction is is 1/Keq
90
Q

Le Chatelier’s principle

A

states that if a stress is applied to a system the system shifts to relieve that applied stress
reaction is temporarily moved out of equilibrium state and responds by reacting in whichever direction to reestablish equilibrium

91
Q

change in concentration

A

add reactants: rxn shifts to right, toward product
add products: rxn shifts to left, toward reactant
remove reactants: rxn shift to left, toward reactant
remove products: rxn shift to right, toward product

92
Q

change in pressure

A

pressure increased: vol decreases, rxn shifts to right toward products
pressure reduced: vol increases, rxn shifts to left toward reactant

93
Q

change in volume

A

volume increased: pressure decreases, rxn shifts to left toward reactant
volume decreased: pressure increases, rxn shift to right toward product

94
Q

change in temperature

A

temperature increases: rxn shifts to left toward reactants

temperature decreases: rxn shifts to right toward products

95
Q

kinetic product

A

the product of a reaction that is formed favorably at lower temperature bc thermal energy is not available to form the transition state required to create a more stable thermodynamic product
has smaller overall different in free energy b/w products and reactants than thermodynamic product
called the “fast” product
minor product

96
Q

thermodynamic product

A

the product of a reaction that is formed favorably at a higher temperature because thermal energy is available to form the transition stat of the more stable product
has a larger overall different in free energy than kinetic product, but is the more stable product bc is has a lower free energy
major product

MCAT (18 decks)

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